(a) Field of the Invention
The invention relates to a power mesh management method, particularly to a macro block power mesh management method.
(b) Description of the Related Art
During the integrated circuit design process, the APR (automatic placement and routing) tool not only helps a circuit designer placing the circuit elements at the suitable locations in the chip easily but also helps the circuit designer managing the power routing. The APR tool has become one of the indispensable tools for the circuit designer.
In general, the APR tool uses two types of blocks to manage the circuit elements. One type of the blocks is the standard cell. As the name implies, the standard cell is a standardized block of specific size and fixed power management method for managing some often-used standard circuit elements, such as: flip-flops, logic gates, and the like. Then, the APR tool can neatly arrange a plurality of standard cells in areas of the chip. The other type is the macro block. A macro block is used to manage some circuit elements of specific function designed by the circuit designer, such as: SRAM, ADC, and so on. In practical applications, as is well known in the industry, the size of the macro block usually depends on the size of the circuit elements for the specific function designed by the designer. The APR tool can also arrange the macro blocks at the suitable locations of the chip automatically.
However, although the APR tool can follow specific routing rules to manage the suitable locations for the macro block and to draw the power mesh for the macro block. (Power mesh is usually placed in the upper metal layers of the circuit.) But, as the APR tool can only handle regular management, detailed management still needs manual adjustments by a designer. Therefore, the APR tool still needs to be improved.
Please refer to FIG. 1 which shows a schematic diagram illustrating the macro block 100 managed by the APR tool according to the prior art. In this example, the macro block comprises the annular power supplying lines 110, 120 and the internal circuitry 130. The annular power supplying lines 110, 120 are of annular structure surrounding the internal circuitry and couple to the various circuit elements of the internal circuitry 130 (not shown in FIG. 1). The power supplying line 110 conducts the external power to the internal circuitry 130 through the power mesh in the upper layer (not sown in FIG. 1). And, the power supplying line 120 also conducts the ground voltage to the internal circuitry 130 through the power mesh in the upper layer (not sown in FIG. 1).
Please note that the above mentioned annular power supplying lines 110, 120, including horizontal direction and vertical direction, are just one example. In practical applications, the power supplying lines of the macro block 100 can be of any shape and are not limited to the annular structure surrounding the internal circuitry 130.
Then, please refer to FIG. 2 which shows the macro block 100 of FIG. 1 and the power mesh 200 located in a layer above the macro block 100. As shown in FIG. 2, the dotted line portion indicates the macro block 100 shown in FIG. 1 (including the annular power supplying lines 110, 120 and the internal circuitry 130) while the continuous line portion indicates the power mesh 200 managed by the APR tool in the prior art. As shown in the figure, the power mesh 200 comprises the horizontal power supplying lines 210 and the vertical power supplying lines 220. The vertical power supplying lines 220 are located in a layer above the horizontal power supplying lines 210. In other words, the power supplying line 110, 120, the horizontal power supplying lines 210 and the vertical power supplying lines 220 are respectively located in different metal layer. The power supplying lines 210 and the power supplying lines 220 are mutually perpendicular to form a matrix. Besides, the power supplying lines 210 include a plurality of power lines 211 and ground lines 212 placed in a mutually interlaced manner while the power supplying lines 220 include a plurality of power lines 221 and ground lines 222 placed in a mutually interlaced manner. Please note that only three sets of power supplying lines 210, 220 are shown in the figure for convenience. In general, when there are more power supplying lines 210, 220, the power meshes formed are denser too.
Besides, please note that the small squares 230 shown in FIG. 2 are the via holes (“vias”)/contact and the via plugs for coupling/connecting the structures of different layers. In one embodiment of the invention, as the power lines 211, 221 correspond to the same electrical property, the power lines 211, 221 couple to each other through the vias and the via plugs 230. On the other hand, as the ground lines 212, 222 also correspond to the same electrical property, the ground lines also couple to each other through the vias and the via plugs 230.
As known by the industry, the power lines 211, 221 couple to the external power (not shown in the figure) and the above mentioned annular power supplying line 110 through the vias and the via plugs at suitable locations for conducting the voltage provided by the external power to the macro block 100. The ground lines 212, 222 couple to the ground voltage and the above mentioned annular power supplying line 120 through the vias and the via plugs at suitable locations for conducting the ground voltage to the macro block 100.
Please note that, since it is necessary to conduct the external power/ground voltage into the macro block 100, the resistance between the external power and the macro block 100 is generally properly designed to obtain better overall circuit performance. The resistance between the external power and the macro block 100 is directly related to the number of the vias and via plugs. As is well known to the industry that, due to the resistance shunting effect, the more is the number of the vias the more is the reduction of the resistance between the external power and the macro block 100.
Hence, the position that can be allocated for the via becomes crucial. As mentioned before, the adjustable range of the resistance becomes larger when there are more allocable positions for the via. Therefore, the routing rule of the APR tool is usually designed to place the via and the via plug for coupling at the overlapping areas of the annular power supplying lines 110/120 and the power supplying lines 210/220, and at the overlapping areas of the power supplying line 210 and the power supplying line 220. However, such a design will cause some problems.
Please refer to FIG. 3 which shows the interconnections of the annular power supplying lines 110, 120 and the power mesh 200 in the layer above the annular power supplying lines 110, 120 through the vias and the via plugs. As shown in FIG. 3, the power supplying lines 210, 220 overlap the annular power supplying lines 110, 120 in areas 240 where the power supplying lines 210, 220 interlace the annular power supplying lines 110, 120 vertically. Therefore, the electrical interconnections among these are provided by the vias and the via plugs located in these vertically interlaced overlapping areas. But, as the power supplying lines 210, 220 in the upper layer overlap the annular power supplying lines 110, 120 in areas 250 where the power supplying lines 210 are parallel to the annular power supplying lines 110, 120. The electrical interconnections among these become a problem.
Please refer to FIG. 4 regarding the possible problems of the electrical interconnections in areas 250 among the power supplying lines 210, 220 and the annular power supplying lines 110, 120. FIG. 4 shows two kinds of situations that may cause problems. The first situation is indicated by the area 251. As the power line 211 of the power mesh 200 overlaps the annular power supplying line 110 of the macro block 100 that is to be coupled in the area 251, the via and the via plug are placed in the overlapping area to form the electrical connections. But, from the vertical cross-section point of view, the via and the via plug form a wall-like structure due to the neighboring parallel relationship. As the other metal routings of the same metal layer cannot pass through this wall-like structure, the flexibility of routing is greatly limited. The second situation is indicated by the area 252. As the ground line 222 of the power mesh 200 overlaps the annular power supplying line 120 of the macro block 100 that is to be coupled in the area 252, the via and the via plug are placed in the overlapping area to form electrical connections. But, the power supplying lines 211 and the annular power supplying line 120 are of different electrical potential and are in parallel overlapping relationship. The area available for the via and the via plug in the area 252 to couple the ground line 222 and the annular power supplying lines 120 becomes greatly limited. Therefore, the resistance of the power mesh cannot be reduced effectively.
Therefore, those who are skilled in the art must develop new routing rules and layout methods to solve the above mentioned problems.